Lost my second DJI drone....this time a Mavic Air 2

[crs06e]

So after losing my Mavic mini in the water, I decided to upgrade to the Mavic Air 2. I purchased a Sealander kit for it but it did not arrive before my fishing trip that I wanted to use the drone on. The primary reason I bought the drone was to film fishing and boating activities so flying over the water is what I do mostly. I was flying the drone around the boat videoing us offshore and everything was going fine. I recorded a circle quickshot video and everything was fine. Then I had the drone hovering about 5 feet above the water off the side of the boat and I selected the dronie quickshot. When I selected it, the drone lowered itself right into the water and sank. I watched the flight log on my phone to verify that I was not touching down on the left joystick and I in fact was not. Any idea what happened?

Once again, I purchased the DJI refresh on this drone but cannot use it because I could not recover the drone. If this was a malfunction of the drone, do you think DJI will replace it?

 

[Hauptmann]

So after losing my Mavic mini in the water, I decided to upgrade to the Mavic Air 2. I purchased a Sealander kit for it but it did not arrive before my fishing trip that I wanted to use the drone on. The primary reason I bought the drone was to film fishing and boating activities so flying over the water is what I do mostly. I was flying the drone around the boat videoing us offshore and everything was going fine. I recorded a circle quickshot video and everything was fine. Then I had the drone hovering about 5 feet above the water off the side of the boat and I selected the dronie quickshot. When I selected it, the drone lowered itself right into the water and sank. I watched the flight log on my phone to verify that I was not touching down on the left joystick and I in fact was not. Any idea what happened?

Once again, I purchased the DJI refresh on this drone but cannot use it because I could not recover the drone. If this was a malfunction of the drone, do you think DJI will replace it?

The surface of water often confuses the bottom sensors on drones into "thinking" they are higher than they are, causing the drone to reduce altitude. For this reason, I never fly my M2P lower than about 25' above water level. Even then, I keep a close eye on it.

Sorry you lost your MA2. When you get your new drone, get State Farm insurance for $70/year. Not all agents issue the policy.

 

[J2ps]

I think Dji recommends 12ft at least. Reason is bottom sensors get reflection of water and things go bad.

 

[Rafale74]

ou tout simplement de mettre du scotch sur les capteurs du dessous si vous l'utiliser souvent au dessus de l'eau comme ça il y a plus de problème.

 

[JAW]

ou tout simplement de mettre du scotch sur les capteurs du dessous si vous l'utiliser souvent au dessus de l'eau comme ça il y a plus de problème.

Translation:
or just put tape on the sensors below if you use it often above the water like that there is more problem.

 

[Von Sparkenhoffen]

I was flying above a river yesterday and noticed mine getting lower to the surface. It was difficult to tell how low as my altitude was reading -1.6m, but it looked below 1m. I'd been flying off a small footbridge, so the quad was below me. It actually looked like it was lowering itself of it's own accord, with no input from me? Trying to get those low water shots really isn't worth it, unless you have 'Refresh', and know it's retrievable! Sorry you've lost it! ?

 

[Motorcycle Rider]

Full up left stick, it will stop the descent, and climb.
I've tried it, works great!
Otherwise it will just keep descending, or else stay up 10' or 15' feet off the water. But always remember that you can make it climb, that is what full up left stick is for.

 

[crs06e]

I posted a thread before about using the sensors above water. It seemed that everyone said keep them on.

Since this is a sensor malfunction issue, do you think DJI will replace the drone?

 

[PhantomFandom]

I posted a thread before about using the sensors above water. It seemed that everyone said keep them on.

Since this is a sensor malfunction issue, do you think DJI will replace the drone?

Not everyone says keep them on. In fact, keeping them on that close to the water is obviously problematic. The best answer is to NOT get that close to the water. If you stay at least 10 to 12 feet above the water then you should not run into issues.

If you were that close to the water, I would generally say it wasn't a sensor malfunction. Rather it was an expected consequence of flying too close to the surface, where the sensors can get very confused. This is explicitly stated in the user manual on page 17, so you wouldn't have much traction in claiming it was a sensor malfunction.

 

[sar104]

I posted a thread before about using the sensors above water. It seemed that everyone said keep them on.

Since this is a sensor malfunction issue, do you think DJI will replace the drone?

It wasn't a sensor malfunction - the VPS height indication was correct and detected the descent into the water. In fact all the sensors (barometric, GPS, optical) detected the descent. IMU0 recorded it, but the active IMU, which was IMU1, disregarded those data and did not register the descent:



So while I would say that flying that close to the water is rather unwise, especially in autonomous modes, it might be worth pointing out to DJI that the active IMU ignored the descent. They might be willing to replace it on those grounds.

 

[InvisibleName]

Here’s the direct quote from the manual, don’t think you’ll have much chance of a sensor failure claim (unless your flight data shows a problem.... as @sar104 has potentially indicated!)

The Vision Systems cannot work properly over surfaces that do not have clear pattern variations. The Vision Systems cannot work properly in any of the following situations. Operate the aircraft cautiously.
a. Flying over monochrome surfaces (e.g., pure black, pure white, pure green). b. Flying over highly reflective surfaces.
c. Flying over water or transparent surfaces.
d. Flying over moving surfaces or objects.
e. Flying in an area where the lighting changes frequently or drastically.

 

[crs06e]

It wasn't a sensor malfunction - the VPS height indication was correct and detected the descent into the water. In fact all the sensors (barometric, GPS, optical) detected the descent. IMU0 recorded it, but the active IMU, which was IMU1, disregarded those data and did not register the descent:

View attachment 105831

So while I would say that flying that close to the water is rather unwise, especially in autonomous modes, it might be worth pointing out to DJI that the active IMU ignored the descent. They might be willing to replace it on those grounds.

So why did it descend in the first place? I was not making it descend.

 

[sar104]

So why did it descend in the first place? I was not making it descend.

The FC did not understand that it was descending.

 

[crs06e]

The FC did not understand that it was descending.

FC?

 

[sar104]

FC?

Flight controller. The brains of the aircraft.

 

[Von Sparkenhoffen]

Flight controller. The brains of the aircraft.

So isn't this a software error and not pilot?

 

[sar104]

So isn't this a software error and not pilot?

That really depends, partly on what you expect in terms of vertical control accuracy and also why IMU1 failed to notice the descent - I was unable to determine the reason for that.

 

[boblui]

This is really weird …..

Firstly, the FC totally ignored all other sensor outputs but just trusted IMU_ATTI_1_baraometer Smooth. There is no sensor fusion in the dronie quickshot mode ?

Secondly, I have always thought that IMU_ATTI_1_baraometer_Smooth is just the smoothed version of IMU_ATTI_1_baraometer_Raw. It’s obviously not the case here.

As the descent was due to screwed-up barometer readings, it has nothing to do with water reflection confusing the sensors but many just quickly jumped to that conclusion.

May be I have missed related reports but I am yet to see a substantiated case ( ie, proved by flight logs ) of drones going into water because of sensors being confused by water in some ways. My M2P has been flown very close to water surface many times and there has been no issue.

 

[fGene]

IMU0 recorded it, but the active IMU, which was IMU1, disregarded those data

sar104, this caught my attention. Could you please explain -- does MA2 have, in fact, two independent IMUs? Or is one of them just a dummy, a programming relict from other Mavic's codebases which were re-used for MA2?

I saw many people criticizing MA2 for having a single IMU (versus other Mavic drones which have 2 IMUs), implying such a setup lacks redundancy and therefore is less safe. I personally disagree with such notion because I have never seen a modern "9-axis" IC failing even in extreme conditions and always wondered about algorithm which would choose one IMU over the other (felt like the software responsible for the switch could be a weak link, compromising safety rather than improving it).

Your analysis of this crash seems to suggest there is indeed some critical programming error related to sensor integration. I am afraid that second IMU, if it truly exists in hardware, may complicate things even further for DJI and will make it more difficult to get rid of bugs.

 

[PhantomFandom]

As the descent was due to screwed-up barometer readings, it has nothing to do with water reflection confusing the sensors but many just quickly jumped to that conclusion.

True that many of us (including myself) made the logical assumption, but that nothing is definite until you look at the flight logs. However, I still contend that it is not a good idea to fly that close to the surface of the water. I have done it myself on only a few occasions but that was with sensors off, hands ready on the sticks, and a direct line of sight horizontal to the surface of the water so I could see the actual distance between the drone and the water at all times.